As is generally known, communication systems often have various types of sensors and/or actuators in communication with a control unit. For example, modern vehicles often have a head unit that is not only a car radio but also acts as a control unit that processes signals from various sensors and sends information to various actuators (e.g., for voice control, hands-free services, emergency roadside assistance, etc.). FIG. 1 schematically shows a vehicle head end 118 with a headend control unit 102 and related peripherals. In this figure, the respective connections between the headend control unit 102 and the Audio ADCs 106, the AM/FM/Bluetooth RF radio 108, and the Audio DACs 112, as well as the connection between Audio DACs 112 and Amplifiers 114, are local connections within the head unit 118, while the connections between the microphones 104 and the Audio ADCs 106 and the connection between Amplifiers 114 and Speakers 116 are remote connections with cables. In this figure, the head unit 118 also includes one or more communication interfaces, represented here by the block 110 (e.g., MOST, CAN, Ethernet, etc.). FIG. 2 shows some exemplary microphone connections as known in the art. FIG. 3 is a schematic diagram showing exemplary automobile microphone cabling in accordance with the head unit shown in FIG. 1. As can be seen, there is an excessive amount of wiring for the microphones, which is expensive and adds to the vehicle weight.
Thus, microphones are being used ever more frequently in vehicles for such things as hands-free systems, voice control of various devices, emergency roadside assistance and other remote services, active noise cancellation, and even in-vehicle communication (e.g., intercom, passenger-to-passenger, and driver-to-passenger communications). In automobiles, one or two microphones are often mounted on or near the rear-view mirror, but there are proposals to mount microphones additionally or alternatively in other structures such as the vehicle headliner, seatbelt straps, and/or headrests. In some proposals, multiple microphones (e.g., digital MEMS microphones) will be used together in each of a number of locations (e.g., three separate microphones or a microphone array with three microphones), for example, for beam-forming or beam-steering.
In some cases, it may be necessary or desirable for the headend control unit to send audio information to various devices in the communication system.
In FIG. 1 a head unit 118 could disintegrate some of its functions and use remote, digital connections with cables for the link between the headend control unit 102 and the Audio ADCs 106, the AM/FM/Bluetooth RF radio 108, and the Audio DACs 112.
Transmission of additional control and status information further extends the functionality and enables features as remote control and remote display.
Typically, the headend control unit requires multiple connectors (or ports) for connecting to the various sensors and/or actuators.
Some existing bus systems include:
MAC Controller based bus systems, such as MOST150 (optical, very expensive, optical cable not practical), MOST50 (electrical, expensive, requires transformers and microcontroller at each node), Flexray (complex, has synchronization issues and bandwidth limitations);
SPDIF/AES3 based bus systems, such as SPDIF (192 kBit/s, 24 bits, Stereo, no multichannel support, expensive cable), Differential (AES3)—differential, no multichannel support), Multi Channel ADAT, AES10-MADI (expensive cable and connectors), E1/T1 (ISDN)—too slow, not enough channels supported), proprietary buses; and
Video+Audio Links such as National Semiconductor's FPD or Inova's APIX. These systems use expensive cables/connectors, are point to point systems and are too expensive for systems that don't require a video link.
A survey of various automotive buses can be found at http://www.interfacebus.com/Design_Connector_Automotive.html.